At the isthmus between dividing chloroplasts in many plants and algae there is an electron-dense band of material called the plastid dividing ring (PD ring). The composition of this PD ring is not known, though it appears to consist of filaments around 4 nm in diameter and which number 5 to 7. In the unicellular alga Mallomonas (Chromophyta), the PD ring is especially prominent. I used the HVEM to obtain detailed images of the Mallomonas PD ring that could supplement what is known from conventional thin-section TEM. In particular, I wanted to have stereo images of the ring in glancing section and in cross section (using 0.3fm serial sections). I hope that such images will reveal new information about the spatial relationship of the ring to the four membranes that surround the chloroplast (of chromophytes) and the filamentous nature of the ring itself.